Update & refactor dark mode (#4114)

## Description:

- The renderer no longer knows what "dark mode" is.
`RenderSettings.dayNight.mode` (`"light" | "dark"`) is gone — passes
read neutral values (`lighting.ambient: number`, `lighting.enabled:
boolean`).
- `render-settings.json` holds the light-mode baseline. Dark mode is
just another override layer, applied the same way as graphics settings
(`darkNames`, `classicIcons`, etc.).
- New `src/client/render/gl/RenderOverrides.ts` exposes two in-place
mutators with matching shapes:
- `applyGraphicsOverrides(settings, overrides)` — replaces the old
`generateRenderSettings`
  - `applyDarkModeOverride(settings, isDark)`
- `ClientGameRunner` regenerates the live settings each time the user
setting changes via `deepAssign(live, createRenderSettings())` + the
override chain. No per-slice copy list, no intermediate object — adding
a new override that touches a new section just works.
- Renamed `dayNight` → `lighting`; collapsed `nightAmbient`/`dayAmbient`
into single `ambient`; renamed `enableLightCompositing` → `enabled`.
- Bumped dark-mode ambient from 0.15 → 0.35 so terrain stays readable.

<img width="1250" height="846" alt="Screenshot 2026-06-02 at 11 47
28 AM"
src="https://github.com/user-attachments/assets/b41e8ffb-6011-4ba0-9e1f-c2a21ff90794"
/>

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

src/client/render/gl/RenderSettings.ts

@@ -1,4 +1,3 @@
-import { GraphicsOverrides } from "./GraphicsOverrides";
 import defaults from "./render-settings.json";
 
 export interface RenderSettings {
@@ -47,10 +46,9 @@ export interface RenderSettings {
     particleStrength: number;
     particleFreshScale: number;
   };
-  dayNight: {
-    mode: "light" | "dark";
-    nightAmbient: number;
-    dayAmbient: number;
+  lighting: {
+    ambient: number;
+    enabled: boolean;
     falloffPower: number;
     falloutLightR: number;
     falloutLightG: number;
@@ -296,46 +294,6 @@ export function createRenderSettings(): RenderSettings {
   return JSON.parse(JSON.stringify(defaults)) as RenderSettings;
 }
 
-/**
- * Generate a fresh RenderSettings by layering user overrides on top of the
- * render-settings.json defaults. Pure — does not mutate any input.
- */
-export function generateRenderSettings(
-  overrides: GraphicsOverrides,
-): RenderSettings {
-  const settings = createRenderSettings();
-  if (overrides.name?.nameScaleFactor !== undefined) {
-    settings.name.nameScaleFactor = overrides.name.nameScaleFactor;
-  }
-  if (overrides.name?.cullThreshold !== undefined) {
-    settings.name.cullThreshold = overrides.name.cullThreshold;
-  }
-  if (overrides.structure?.classicIcons === true) {
-    // Classic look: lighter player-colored shape behind a dark icon glyph,
-    // with a touch of translucency.
-    settings.structure.borderDarken = 0.7;
-    settings.structure.fillDarken = 1.0;
-    settings.structure.iconR = 0;
-    settings.structure.iconG = 0;
-    settings.structure.iconB = 0;
-    settings.structure.iconAlpha = 0.75;
-  }
-  if (overrides.name?.darkNames !== undefined) {
-    const dark = overrides.name.darkNames;
-    // Dark: black fill + player-colored outline. Force outline RGB to black
-    // so the shader's defaultFill ramp (mix(uOutlineColor, black, fillT))
-    // collapses to pure black regardless of ambient.
-    // Colored: player-colored fill + white outline (defaults from JSON).
-    settings.name.fillUsePlayerColor = !dark;
-    settings.name.outlineUsePlayerColor = dark;
-    const channel = dark ? 0 : 1;
-    settings.name.outlineR = channel;
-    settings.name.outlineG = channel;
-    settings.name.outlineB = channel;
-  }
-  return settings;
-}
-
 /** Dump current settings to a downloadable JSON file. */
 export function dumpSettings(settings: RenderSettings): void {
   const json = JSON.stringify(settings, null, 2);